Light-induced expression of genes involved in phenylpropanoid biosynthetic pathways in callus of tea (Camellia sinensis (L.) O. Kuntze)

Tea (Camellia sinensis (L.) O. Kuntze) is a commercially important crop that is valued for its secondary metabolites. Light is an important environmental parameter that regulates plant growth and development and influences the phenylpropanoid metabolism in plants. To investigate the molecular mechanism by which light regulates phenylpropanoid metabolism, we established light-induced suppression subtractive hybridization (SSH) cDNA libraries of tea calli. A total of 265 clones from the library were selected, sequenced, and analyzed in this study. Nine diverse ESTs involved in phenylpropanoid biosynthesis were detected in the library. A new CsDFR gene (CsDFR2), higher increment of the expression activated by light than the previously reported CsDFR gene (CsDFR1), was cloned. The key phenylpropanoid compounds and representative genes expression analysis implied that light could be effective for activation of the biosynthesis of phenylpropanoids. Compared to the darkness control, levels of lignins, catechins, and PAs were increased 3.46, 3.00, and 1.21-fold, in light-induced calli, respectively. And lignin biosynthesis genes, involved in CCoAOMT, HCT and CCR, were identified in the light-induced SSH library. Therefore it was assumed that lignins might be the main phenylpropanoid metabolites activated by light in tea calli. In addition, our researches found that catechins, as the main secondary metabolites, significantly decreased in the tea calli compared to those in tea mature leaves, While PAs (polymer of catechins) in calli did not decrease compared to mature leaves. The data suggest that polymerization reaction might be the main pathway of flavonoid metabolism in tea callus. The SSH library established in this study represents a valuable resource for better understanding the mechanisms of light-induced secondary metabolism in tea plants.

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► We established tea light-induced SSH cDNA libraries.
► A new CsDFR gene of tea was cloned.
► Light can activate the biosynthesis of phenylpropanoids.
► Lignins are the main phenylpropanoid metabolites activated by light in tea calli.
► Polymerization reaction of catechins is the main pathway of flavonoid metabolism in tea callus.